1. Field of the Invention
This invention relates to an internal valving control mechanism within a damper for a vehicle. More particularly, this invention relates to an internal valving mechanism to control damping fluid in channels within the piston rod of a damper, such as a shock absorber or a MacPherson strut.
2. Prior Art
In one typical suspension system for automobiles, shock forces are "absorbed" by a spring and shock absorber combination. The shock absorber consists of a rod and piston mounted within an outer cylinder, and the spring urges the rod to extend outwardly from the outer cylinder. Vibrations transferred from the vehicle wheel in contact with the road surface are "absorbed" by the compression and extension of the spring. Spring rebound and compressions, however, must be damped to prevent the spring from a series of extensions and contractions that would otherwise be caused by the vehicle wheels traversing road surface irregularities. Shock absorbers provide the damping needed.
One typical shock absorber has an oil cavity in the cylinder on each side of the piston within the cylinder. Compression of the shock absorber (as the spring and piston rod are compressed in response to contact of the wheel with the road) forces oil from one cavity into the other, and rebounding is subsequently damped by the resistance of oil flow in the "reverse direction as the piston is urged toward extension by the rebounding force of the spring. The valving within the piston and between the cavities thus provides the appropriate resistance to fluid flow between the two cavities.
For example, various types of check valves have been developed to allow fluid flow in compression (from the cavity beneath the piston through or around the piston head and into the outer cylinder reservoir cavity) more freely, i.e., with less resistance, than in extension (from the outer reservoir cavity and from the cavity surrounding the rod into the cavity beneath the piston). Such check valves thus provide greater damping when desired, during extension (rebound), rather than during compression shock absorption, when the shock absorber should compress relatively freely.
Improvements on this basic arrangement have provided varying damping characteristics for varying road conditions or vehicle speed, load, or acceleration. As a vehicle goes faster, for example, the damping should often be increased to counteract the increased forces that tend to reduce contact between the tire and the surface of the road.
One such variable damping shock absorber is shown in U.S. Pat. No. 4,527,676 issued Jul. 9, 1985 to Emura et al. The Emura patent discloses a shock absorber with variable damping accomplished by a motor rotating a four-way check valve in the shock. The motor is either (1) a step motor with four steps, one for each of the possible orientations of a four-way check valve, or (2) a feedback-controlled motor, with four arcuate electrical leads contacted by brushes to determine the exact position of the motor drive. Both types of motors are relatively complicated and expensive, as is the four-way valving associated with each.
For example, the Emura device requires a four-wire harness. Many of today's cars, however, are designed with harnesses having no more than two wires available for use by variable damping shock absorbers. Thus, the four-wire harness of Emura would require a costly re-design of wiring harnesses already existing and prevalent in the market.
Another problem with the Emura device is its relatively complicated and expensive motor mechanism. In the embodiment utilizing a four-way step motor, such motors are inherently complicated and expensive because they must be adapted to stop at each of four points, with appropriate electronics to maintain control of the position of the stop motor at each of its four stop positions.
In Emura's embodiment utilizing a feedback-controlled motor, the motor provides four-way stepping through a feedback control circuit which receives the feedback from mechanical wipers brushing over electrical contacts. These wipers and contacts wear and corrode over time, causing loss of electrical contact. Emura's variable damping mechanism can thus completely fail long before likely breakdown from any of the remaining components.
In addition, shock absorbers such as Emura necessarily require an electrical wire connection between the shock absorber internal structure and the external source of electrical energy. In the exposed and high impact area of a vehicle suspension type shock absorber, the wire leads from the vehicle to the shock absorber are thus at risk of corroding or breaking altogether.